1.tomcat5下jsp出現(xiàn)getOutputStream() has already been called for this response異常的原因和解決方法在tomcat5下jsp中出現(xiàn)此錯(cuò)誤一般都是在jsp中使用了輸出流（如輸出圖片驗(yàn)證碼，文件下載等），
沒(méi)有妥善處理好的原因。
具體的原因就是
在tomcat中jsp編譯成servlet之后在函數(shù)_jspService(HttpServletRequest request, HttpServletResponse response)的最后
有一段這樣的代碼
finally {
if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context);
}
這里是在釋放在jsp中使用的對(duì)象，會(huì)調(diào)用response.getWriter(),因?yàn)檫@個(gè)方法是和
response.getOutputStream()相沖突的！所以會(huì)出現(xiàn)以上這個(gè)異常。
然后當(dāng)然是要提出解決的辦法，其實(shí)挺簡(jiǎn)單的（并不是和某些朋友說(shuō)的那樣--
將jsp內(nèi)的所有空格和回車(chē)符號(hào)所有都刪除掉），
在使用完輸出流以后調(diào)用以下兩行代碼即可：
out.clear();
out = pageContext.pushBody();
最后這里是一個(gè)輸出彩色驗(yàn)證碼例子（這樣的例子幾乎隨處可見(jiàn)）
imag.jsp
<%@ page import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%@ page import="java.io.OutputStream" %>
<%!
Color getRandColor(int fc,int bc){
Random random = new Random();
if(fc>255) fc=255;
if(bc>255) bc=255;
int r=fc+random.nextInt(bc-fc);
int g=fc+random.nextInt(bc-fc);
int b=fc+random.nextInt(bc-fc);
return new Color(r,g,b);
}
%>
<%
try{
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
OutputStream os=response.getOutputStream();
Graphics g = image.getGraphics();
Random random = new Random();
g.setColor(getRandColor(200,250));
g.fillRect(0, 0, width, height);
g.setFont(new Font("Times New Roman",Font.PLAIN,18));
g.setColor(getRandColor(160,200));
for (int i=0;i<155;i++)
{
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(12);
int yl = random.nextInt(12);
g.drawLine(x,y,x+xl,y+yl);
}
String sRand="";
for (int j=0;j<4;j++){
String rand=String.valueOf(random.nextInt(10));
sRand+=rand;
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
g.drawString(rand,13*j+6,16);
}
session.setAttribute("rand",sRand);
g.dispose();
ImageIO.write(image, "JPEG",os);
os.flush();
os.close();
os=null;
response.flushBuffer();
out.clear();
out = pageContext.pushBody();
}
catch(IllegalStateException e)
{
System.out.println(e.getMessage());
e.printStackTrace();
}%>
如有不足之處，歡迎斧正！
2
getOutputStream() has already been called for this response問(wèn)題的解決
在jsp向頁(yè)面輸出圖片的時(shí)候,使用response.getOutputStream()會(huì)有這樣的提示：java.lang.IllegalStateException:getOutputStream() has already been called for this response,會(huì)拋出Exception
原因一:
JSP默認(rèn)的輸出流為PrintWriter ,即<% %>以外的東西所默認(rèn)的輸出方式,如果你嘗試在JSP中使用ServletOutputStream就會(huì)引起錯(cuò)誤.要嘛直接改用Servlet輸出(復(fù)寫(xiě)service方法),要嘛刪除除%><%中的任何東西
(包括HTML標(biāo)簽,空格,回車(chē)等東西)應(yīng)該就可以。
對(duì)于這樣的情況應(yīng)該這樣來(lái)解決，刪除%><%之間的所有內(nèi)容包括空格和換行符，最后也要消除空格和換行符，
最好再加上一句response.reset()。
原因二:
在J2EE的API參考里有這么個(gè):
ServletResponse的getWriter()方法里會(huì)拋出這個(gè)異常,
IllegalStateException - if the getOutputStream method has already been called
for this response object
而它的getOutputStream()方法里會(huì)拋出這個(gè)異常.
IllegalStateException - if the getOutputStream method has already been called for this response object
并且兩者的函數(shù)申明里都有這么樣的一句
Either this method or getOutputStream() may be called to write the body, not both.
Either this method or getWriter() may be called to write the body, not both.
以上說(shuō)明也解釋了為什么在往頁(yè)面中寫(xiě)入圖片的時(shí)候要使用如下循環(huán)格式
OutputStream output=response.getOutputStream();
while((len=in.read(b)) >0)
{
output.write(b,0,len);
}
output.flush();
而不是把response.getOutputStream().write()放到循環(huán)體內(nèi)
在頁(yè)面中直接寫(xiě)：
<body bgcolor="#ffffff">
<h1>
<%
response.getOutputStream();
%>
</h1>
</body>
將會(huì)出現(xiàn)錯(cuò)誤消息如下：
java.lang.IllegalStateException: getOutputStream() has already been called for this response
org.apache.catalina.connector.Response.getWriter(Response.java:604)
org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)
org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)
org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)